In processes of mining ores containing useful uranium, it is usual to adopt a process of selective leaching or uranium from the ore, followed by selective separation of uranium from the rest of the cations using ion exchange or solvent extraction. A waste slurry results, as a process by-product, which is discarded into tailings ponds. The ore may contain as little as 0.85 kg of U.sub.3 O.sub.8 per ton. Consequently the amounts of waste liquid and solids to be discarded are very large. Whilst in general the disposal practices in the uranium mining and milling industry are similar to those in other mining and milling operations and are relatively efficient, uranium presents particular problems on account of its radioactive end-product and wastes, and on account of the fact that other radioactive materials are normally found associated with uranium ores.
It is estimated that only about 15% of the total radioactivity of the initially mined ore mixture leaves with the final uranium containing product, the remaining 85% being discharged in the tailings.
Another problem arises from the presence of thorium in uranium ores. Thorium is present in Canadian uranium ores in ratios ranging approximately from ThO.sub.2 /U.sub.3 O.sub.8 =0.15 to 0.60. All twelve known thorium isotopes are radioactive. Thorium is not generally recovered from the bearing ores, and is merely discharged with the tailings. Thus the radioactivity of the thorium adds to that of the uranium and other radionucleides and both end up in the surface waters and environment.